The present invention relates to clamps for holding a circuit card assembly in a chassis, and more particularly to a clamp for electrically seating a circuit card assembly in a chassis and for thereafter establishing thermal contact between the circuit card assembly and the chassis by the lateral expansion of thermally conductive wedges.
A circuit card assembly (CCA) is a replaceable package of electronic components mounted on a substrate. Other terms used to identify a CCA are "electronic circuit module", "circuit board", "wiring board" and the like. Typically, a plurality of CCAs are carried by a chassis, that is also referred to as a "rack".
The electronic components on the CCA may generate heat that must be conducted from the components to prevent damage due to overheating. The CCA substrate conducts the heat away from the components, and the chassis is a heat sink for the CCA substrate.
Typically, clamps are used to urge the CCA against the chassis and into a thermally conductive relationship to facilitate thermal conduction therebetween. Some conventional clamps do not conduct an appreciable amount of heat from the CCA to the chassis because of small thermally conductive surface areas in contact with the CCA and the chassis, and, when the clamps include a plurality of short sliding surface wedges, because of small thermally conductive surface areas of wedge-to-wedge contact. See, for example, U.S. Pat. No. 4,823,951 to Colomina, especially FIG. 5. More recent wedge clamps enhance thermal conductivity by providing thermally conductive surfaces that extend substantially the length of one side of the CCA, as shown, e.g., in U.S. Pat. No. 4,971,570 to Tolle, et al.
Clamps are also used to insert a CCA into and to extract a CCA from a chassis. In some CCAs, a substantial force may be required to seat the CCA to make the required electrical connection, i.e., to insure that the CCA is properly seated, and it is desirable that the insertion force be controllable by the user to avoid damage to the chassis or to the CCA.
Clamps that both seat a CCA and provide some thermal conductivity are also known. However, such clamps do not provide the full capability of single purpose clamps, generally have a small thermally conductive surface area and do not provide a controllable insertion force which is selectively variable. Moreover, they may be difficult to operate, maintain and manufacture. For example, the clamp in U.S. Pat. No. 4,821,147 to Jacobs, et al. includes a shape memory alloy that is heated to automatically and sequentially insert the CCA and expand the wedges.
Accordingly, it is an object of the present invention to provide a novel clamp and method that obviates the problems of the prior art and operates simply to both seat a CCA and urge thermal conductivity between the CCA and a chassis.
It is another object of the present invention to provide a novel clamp and method in which the forces of CCA insertion and wedge expansion are selectively variable independently of one another.
It is yet another object of the present invention to provide a novel clamp and method which does not require either electrical or thermal controls in the insertion of the CCA into the chassis and in the expansion of the wedges.
It is a further object of the present invention to provide a novel clamp and method in which a single shaft is used to independently seat a CCA to insure an electrical connection and to expand the two wedges that provide for heat transfer.
It is still a further object of the present invention to provide a novel clamp and method in which a single shaft effects longitudinal motion of one wedge to seat a CCA and a nut on the shaft effects longitudinal motion of a cooperating wedge to urge the CCA into a thermally conductive relationship with the chassis.
It is yet a further object of the present invention to provide a novel clamp and method in which a clamp that seats a CCA in a chassis with a controllable force also provides thermal conductivity through the clamp over a substantial portion of a length of a side of the CCA.
These and many other objects and advantages of the present invention will be readily apparent to one skilled in the art to which the invention pertains from a perusal of the claims, the appended drawings, and the following detailed description of preferred embodiments.